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Biotite

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A grouping of lustrous black biotite crystals measuring 3.2 x 2.5 x 2.0 cm in size set on a massive calcite matrix. In good condition, a choice example for the species.The Otter Lake area in the Pontiac RCM of the Outaouais region, Quebec, Canada, lies within the Central Metasedimentary Belt of the Grenville Geological Province. Its geology is defined by Precambrian high-grade metamorphic rocks, including calc-silicate skarns, marble units, and granite pegmatites intruding surrounding biotite-bearing gneisses. Historical interest in the area grew during the middle of the twentieth century with the exploration and development of local uranium and thorium deposits, most notably at the famous Yates Mine. Small-scale mining and extensive field prospecting gave way to active mineral collecting, as the region became well known for producing sharp crystals embedded in coarse matrix. Within these skarn and pegmatitic zones, biotite is widespread as dark brown to black lustrous sheets and tabular book-like crystals, frequently associated with scapolite, diopside, fluorapatite, and calcite.